1. Field of the Invention
The present invention relates in general to a shower head used in dry etching process, and more particularly, to a manufacturing method and an improved structure of anti-corrosion shower head used in dry etching process.
2. Description of the Related Art
In the chamber of a dry etching process, a shower head is used for spraying an etching gas. Referring to FIG. 1A, it is a front view of a conventional shower head. The shower head 100 consists of a large cross-shaped aluminum base 102 and a small cross-shaped ceramic nozzle plate 104, wherein the aluminum base 102 has a front side and a rear side while the ceramic nozzle plate 104 is embedded at the center of the front side of the aluminum base 102. Referring to FIG. 1B, it is a rear view of the shower head in FIG. 1A. There are a number of gas holes formed on the rear side 108 of the aluminum base 102, which the positions of the gas holes are corresponding to the ceramic nozzle plate 104, to spray the etching gas.
The conventional shower head 100 is electroplated in the solution of sulphuric acid (H2SO4) to coat an Al2O3 film on the aluminum surface. Such treatment is well known as “hard anodizing treatment”. Normally, the Al2O3 film coated by the electroplating solution of sulphuric acid has a thickness of 45˜55 μm. In the chamber of dry etching process, plasma is generated and maintained via a high power radio frequency (RF). Moreover, all the gases, such as SF6, Cl2, BCl3 and HCl, used in the dry etching process are corrosive. Taking SF6, a nontoxic etching gas, as the example, corrosive fluoride ions will be produced after SF6 is de-ionized via a high power radio frequency. The Al2O3 film formed on the aluminum surface of the shower head is plasma resisting and corrosion resisting as well.
Although the front side 106 of the shower head 102 has a cross-shaped ceramic nozzle plate 104, the rear side 108 of the shower head 102 is still an aluminum substrate. Also, very low pressure (about 2 mtorr) and high power radio frequency is applied when the shower head 102 is operated. Thereby, the corrosive etching gas sprayed through the gas holes 110 in a certain velocity of flow will corrode the central part of the rear side 108 of the shower head 102 and gas holes 110 as well. The serious corrosion damage occurs on the sharp edges of the gas holes 110, especially.
Referring to FIG. 2A, it is a side view of a single gas hole covered by an Al2O3 film. The gas hole 200 of the unused shower head 100 has a complete and even Al2O3 film 202. It is noted that the Al2O3 film 202 on the sharp corners of the gas hole is thinner on that on the lateral sides. Referring to FIG. 2B, it is a side view of a single gas hole after parts of the Al2O3 film has peeled off. After the shower head 100 has been used over a period of time, the Al2O3 film starts to peel off due to plasma collision and etching gas corrosion. The peeling off phenomena is first started at the sharp corners 204 of the gas hole; so as to expose the sharp corners 204 to the air.
The Al2O3 film coated on the aluminum surface has the function of anti-corrosion and insulation. If a high radio frequency is applied, the air surrounding the exposed sharp corners 204 of the gas hole will be ionized and discharged. This phenomenon is called the “point discharge”, which always results in short-circuit. Despite that the shower head is recoated or the sharp corners 204 of the gas hole are rounded, corrosion still occurs after a while. Besides, the particle issue, which arises due to corrosion, will influence the yield of the product. Generally, the shower head needs to be cleaned and maintained (PM) in about one week, and needs to be replaced in a fortnight's time. In other words, the shower head has a PM cycle time of about one week's time while its service life is about two weeks' time. Also, it is very exhausting and time-consuming to clean and maintain the shower head. The detached shower head needs to be immersed in isopropyl alcohol (IPA), otherwise, the acid gas, which stays on the surface of the detached shower head, will react with the moisture contained in the air and become a strong acid. After the IPA immersion, the shower head needs to be purged by nitrogen gas, and dried for 30 minutes at a high temperature. The cleaning process in a round takes at least 8 hours.
According to the description above, a conventional shower head used in the etching process of will be corroded in a short period of a time. It requires not only the cleaning process but also the replacement of the shower head. The frequent replacement of expensive shower heads is a great burden to semi-conductor manufacturers. Moreover, the particle issue arising due to corrosion further reduces the yield of products.